Published 07/08/2014

Sogefi composite coil spring to be launched by Audi for 2015

Jointly developed glass fiber reinforced polymer (GFRP) coil springs save 40 to 70 percent weight vs. steel.

Edited by: CW Editorial Team

Sogefi (Milan, Italy) has developed jointly with automaker Audi (Ingolstadt, Bavaria, Germany) a patented coil spring technology using fiber reinforced composites. Scheduled to introduce the new technology in an upper mic-size model before year‐end, Audi will be the world’s first car manufacturer to launch this technology in series production.

Sogefi, reportedly one of the world leaders in filtration systems and flexible suspension components as well as air management and engine cooling systems, has patented this new type of coil spring made from glass fiber reinforced polymer (GFRP) which weighs between 40 and 70 percent less than traditional steel springs. The new GFRP coil springs can be assembled on cars and light commercial vehicles without affecting the suspension system architecture and allow for a weight reduction of 4 to 6 kg (9 to 13 lb) per vehicle — depending on coil spring design and vehicle type — as well as a significant reduction in the unsprung mass. The resulting benefits range from more precise driving, lower fuel consumption with consequent reduction in CO2 emissions (up to 0.5 g/km), enhanced noise‐vibrational‐harshness (NVH) comfort and full protection against corrosion.

Guglielmo Fiocchi, CEO of Sogefi, commented: “Research and development is a key factor for the future growth of Sogefi. Innovation in the car sector, starting from reducing weight and improving the efficiency of vehicles, now depends significantly on the components companies. Sogefi in particular is gradually increasing its investment in research and development, which has gone up in recent years from around 2 percent to just under 3 percent of its total revenues. We are very proud of the choice that Audi has made”.

Sogefi claims this innovation also guarantees a significant reduction of CO2 emissions during the manufacturing process as the overall energy required is significantly lower than in traditional steel coil spring manufacturing.

Car and Driver reports that the spring is easily differentiated from typical steel springs by its light green color, slightly larger overall diameter, and lower number of coils. It describes how the core of the spring is made from long glass fibers, which are twisted together and impregnated with an epoxy resin. The core is then wrapped with additional glass fibers using a special machine that enables application at alternating angles of +/- 45° relative to the longitudinal axis. Car and Driver explains that these layers meet tension and compression loads, supporting one another to optimally absorb the stresses acting on the spring. Once assembled, the epoxied blanks make a trip through a 212ºF oven for final curing.

Audi reports that it can precisely tune the composite springs and points out that the material will not corrode, even after acquiring road debris, and are impervious to chemicals such as wheel cleaners. Car and Driver sums up its report by noting that the concept of a composite spring is not new. Chevrolet introduced the fully composite-sprung C4 Corvette in 1984, but unlike the Audi’s composite coils, which will replace the steel springs at all four corners, the Corvette featured a single transverse leaf spring at the front and rear. Reportedly, the current C7 Corvette Stingray still uses the same leaf-spring setup.